This project is designed to investigate the mechanisms by which normal body temperature is altered when man and animals become infected by pathogens that cause a cardinal sign of disease-fever. The objectives of the current proposal are to develop and investigate a murine model of the fever process; to use this model to understand the interactions between the immune system and the central nervous system to gain a more thorough understanding of the role of fever in the host-defense response to injury and infection. There are 4 specific aims in the proposal: (1) To examine the anatomical location and cellular site of action of the blood-borne cytokine interleukin-1 (IL-1) in the circumventricular organ (CVO) known as the OVLT, in the production of prostaglandin E (PGE) and its subsequent induction of the febrile response via stimulation of the thermoregulatory pathways within the CNS. (2) Investigate the mechanism whereby immunoadjuvant treatment enhances the febrile sensitivity of rats to IL-1. (3) Use the rat fever model to investigate functional connections between the immune aspects of the host-defense response to infection and the pathogenesis of fever and explore the modification of these responses by immune stimuli such as interferon-g and immunoadjuvants. Explore the connection between Ia antigen and fever sensitivity. (4) Develop and investigate the more general hypothesis that a role of PGE release by IL-1 at the blood/brain interface within the CVO's is an immunosuppression of the interaction between circulating pathogens and the CNS. These objectives will be accomplished by a variety of experimental protocols outlined in the proposal that include: Measuring febrile responses and responsiveness of the animals in a partitional calorimeter in response to cytokines. Measuring in vitro binding of labeled Il-1 ligands to CVO receptor sites exposed on frozen section cut from rat brain. Measuring in vitro release of endogenous PGE in response to IL-1 stimulation of OVLT punched from the brain tissue. Comparing binding affinities of labeled IL-1 in the OVLT and neuropil before and after immunoadjuvant treatment in rats. Measuring the incidence of Ia antigen expression on cells that respond to IL-1 stimulation and comparing the effects of immunoadjuvant treatment on Ia expression with the subsequent increase in febrile sensitivity of rats to intravenous injections of IL-1. Cytolizing Ia antigen expressing cells in the OVLT with antibody to Ia and ascertaining the effect of this treatment on subsequent febrile sensitivity to IL-1. Measuring the binding of labeled IL-1 ligands and the release of endogenous PGE by the 7 CVO's of the brain on frozen brain tissue slices and punches. Remove the IL-1 binding cells from fresh OVLT microdissection punches, by trypsin dispersion and attempt to culture these cells in vitro, so that their responses and interactions with cytokines can be studied more completely and fully. It is anticipated that the information gained from these studies will provide new insights into the role of fever in the host- defense response and expand our understanding of the relationship between the immune system and the central nervous system. This project has direct implications for the treatment of many diseases in man and animals.